Recently, organic EL displays have attracted attention as the next-generation flat display panels. The organic EL displays have such advantages as self-luminescence, wide viewing angle, high-contrast image, thin profile, lightweight, and low power consumption.
Each of the organic EL devices that constitute an organic EL display generally includes a pixel electrode, a counter electrode, and an organic layer disposed between the pixel electrode and counter electrode. The organic layer is composed of a light-emitting layer containing fluorescent molecules, and an electron conductive thin film and a hole conductive thin film which sandwich the light-emitting layer. Application of voltage between the counter electrode and the pixel electrode results in the injection of electrons into the electron conductive thin film from the counter electrode and injection of holes into the hole conductive thin film from the pixel electrode, with the result that the electrons and holes are recombined in the light-emitting layer to cause luminescence.
A manufacturing method of an organic EL display includes lamination of organic layers and thin-film electrodes, which are of the order of several tens of nanometers. This lamination process is conducted in a clean room. Nevertheless, it is not possible to completely rid the clean room of foreign material such as particles derived from an organic layer manufacturing machine or other device or from the surrounding environment. Thus, foreign material may be incorporated into the organic layer during manufacture of an organic EL display.
When voltage is applied between the pixel electrode and counter electrode in a state where an organic layer is contaminated with foreign material, it results in current leakage between the electrodes via the foreign material. Current leakage results in low luminous efficiency, leading to high power consumption. Moreover, in a pixel contaminated with foreign material, current leakage via the foreign material reduces the current flow in the organic layer (light-emitting layer) of the pixel. This reduces the overall brightness of the light-emitting layer of the pixel. The presence of pixels contaminated with foreign material causes brightness variation across the organic EL display.
Known techniques for preventing current leakage via foreign material incorporated into the organic layer include laser repair method. The laser repair method is a process whereby current leakage via foreign material is prevented by laser irradiation of a portion of organic layer contaminated with foreign material (hereinafter also referred to as a “defect”) (see, e.g., Patent Literatures 1 to 12).
Patent Literature 1 discloses a method in which a laser beam is applied to the pixel electrode of a defective organic EL device having a color filter, so that multi-photon absorption occurs only at the pixel electrode. This allows for selective destruction (insulation) of the pixel electrode in the defect without causing destruction of other components such as a color filter, making it possible to avoid current leakage between the pixel electrode and counter electrode via the defect.
Patent Literatures 2 to 5 disclose a method of preventing current leakage via foreign material by laser ablation of either of a pixel electrode or counter electrode at a defect.
Patent Literature 6 discloses a method of insulating an electrode at a defect by oxidizing the electrode by laser irradiation. Insulation of the defect makes it possible to prevent current leakage via foreign material.
Patent Literatures 7 to 9 disclose a method of preventing current leakage via foreign material by insulating the foreign material itself in the defect by laser irradiation.
Patent Literatures 10 to 12 disclose a laser repair device having a controller and a beam generator. The disclosed laser repair devices are configured to identify the position of a defect present in an organic EL display panel by means of the controller and to irradiate the defect with a laser beam by means of the beam generator for insulating the defect, so that the organic EL display panel can be repaired.